The block copolymers up to now applied in general in bituminous compositions for road applications, were composed of terminal poly(vinyl aromatic) blocks and poly(butadiene) and/or poly(isoprene) central blocks. Said block copolymers had a linear structure e.g. S—B—S or S—I—S, or a radial structure e.g. (SB)nX or (SI)nX, wherein S represented a poly(vinyl aromatic) block, B represented a poly(butadiene) block and I represented a poly(isoprene block, wherein X was the residue of a coupling agent and wherein n was an integer having a value of at least 3 and in particular in the range from 3 to 10.
Although said block copolymers, containing poly(butadiene) or poly(isoprene) central blocks have shown attractive high low temperature properties in bituminous blends which were maintained over time, providing an acceptable estimated service life, an experienced disadvantage of said block copolymers in bituminous compositions, was a significant viscosity increase after storage at high temperatures e.g. 180–200° C., which made the bituminous compositions difficult manageable after hot storage.
Moreover gel formation was encountered in bituminous compositions, composed in particular of S—B—S, after 70 hours or more storage at said higher temperatures. It will be appreciated that there is a clear need to eliminate or diminish such viscosity increase and gel formation, which deteriorate an efficient end-use processing of the bituminous blends. Therefore it is an object of the present invention to provide better processable bituminous compositions, comprising block copolymers, after storage at higher operation temperatures.